One type of display device which is now in wide use is a gas plasma display panel which contains cathodes and anodes, and a cathode is caused to glow and represent a character when an electrical potential is connected between it and an anode. In panels of this type, mercury is provided in the gas to prevent cathode sputtering. However, when these panels are used in a low temperature environment, the mercury condenses out of the gas and is thus not available to perform its function. In addition, when the mercury condenses, it may adversely affect the part of the panel on which it condenses, for example, by shorting adjacent electrodes.
In the past, the problem of mercury condensation has been solved by providing a heater external to a panel for heating the panel and the mercury therein. Also, U.S. Pat. No. 4,520,290 describes a display panel having an internal heater strip. The disadvantages of the external heater are discussed in the patent and they are rather obvious. The panel described in the patent has the disadvantage that it does not teach of means for adjusting the resistance of the heater strip during manufacture of the panel, in fact the patent provides no teaching as to how the required resistance is achieved and how compensation for variations in manufacture can be achieved. In addition, the panel in the patent provides globules of mercury in the panel and these are heated by the heater strip. This does not avoid the problem of internal mercury shorting and does not provide desirable control of the mercury.
The present invention solves the foregoing problems by providing heater means in a gas filled display panel wherein the heater means can be controlled and adjusted easily during the manufacture of the panel to achieve the desired heating capability thereof. In addition, the heater means is positioned so that it heats mercury in the panel and the mercury source located in a tubulation secured to the outside of the panel to provide control of the mercury admitted to the panel. There are no globules of mercury in the panel which might cause electrical shorts.